A fuel cell has been proposed as a clean, efficient and environmentally responsible power source for electric vehicles and various other applications. Individual fuel cells can be stacked together in series to form a fuel cell stack. The fuel cell stack is capable of supplying electricity sufficient to power a vehicle. In particular, the fuel cell stack has been identified as a potential alternative for the traditional internal-combustion engine used in modern automobiles.
One type of fuel cell is the polymer electrolyte membrane (PEM) fuel cell. The PEM fuel cell includes three basic components: a pair of electrodes, including a cathode and an anode; and an electrolyte membrane. The electrolyte membrane is sandwiched between the electrodes to form a membrane-electrode-assembly (MEA). The MEA is typically disposed between porous diffusion media, such as carbon fiber paper, which facilitates a delivery of reactants such as hydrogen to the anode and oxygen to the cathode. In the electrochemical reaction of the fuel cell, the hydrogen is catalytically oxidized in the anode to generate free protons and electrons. The protons pass through the electrolyte to the cathode. The electrons from the anode cannot pass through the electrolyte membrane, and are instead directed to the cathode through an electrical load, such as an electric motor. The protons react with the oxygen and the electrons in the cathode to generate water.
The fuel cell stack including a plurality of individual fuel cells may be disposed adjacent an end unit. The end unit may include a plurality of main bodies secured together through the use of any conventional method such as fastening or adhesion. Alternately, the end unit may include a single main body. The main body may house fuel cell subsystems and related devices that aid in the preconditioning and operation of the fuel cell stack. As nonlimiting examples, the fuel cell subsystems and related devices housed within the main body can include end plates, fluid passages, e.g. hydrogen fuel and oxidant (O2/air) passages, coolant pumps, recirculation pumps, drainage valves, fans, compressors, valves, electrical connections, reformers, humidifiers, water vapor transfer units, heat exchangers, and related instrumentation. It should be recognized that additional fuel cell subsystems and related devices used in support of the fuel cell system can also be housed in the main body.
The fuel cell subsystems and related devices housed within the main body may contain a plurality of cavities within the fuel cell subsystems and related devices. The cavities may be a result of manufacturing processes, weight reduction, or a desired arrangement of the fuel cell subsystems and devices. While the cavities greatly decrease the thermal mass of the end unit, the cavities significantly increase an internal surface area of the end unit, promoting excessive heat transfer around and between the fuel cell subsystems and related devices within the end unit. Excessive heat transfer to an operating environment of the end unit may also occur. Excessive heat transfer occurs when an external surface area of the end unit is at a higher temperature than the operating environment. A vehicle compartment is a nonlimiting example of the operating environment. Heat transfer may result in the loss of large amounts of heat energy from the end unit. When the end unit is at a temperature below an optimal starting temperature for a fuel cell stack, heat energy lost to the thermal mass of the end unit may increase the time required for the fuel cell stack to reach a full operating potential.
Insulating the end units of the fuel cell stack is known as a method of reducing energy losses. Insulating wraps have been used to insulate the fuel cell stack end unit. While effective at militating against excessive heat energy loss, the insulating wraps are not without disadvantages.
The insulating wraps added to the end unit of the fuel cell stack increase an overall size of the end unit. The fuel cell stack having a compact size is a desired quality, and in vehicle applications, space is at a premium. A method of insulating the end unit of the fuel cell stack without increasing the overall size of the end unit nay be very desirable to a vehicle manufacturer.
The fuel cell stack may require maintenance with repeated use. For the maintenance to be conducted, the fuel cell stack may need to be disassembled to provide access to the individual fuel cells or the fuel cell subsystems and related devices. Prior to end unit removal, the insulating wraps may need to be removed. The insulating wraps, which may be fragile and prone to excessive wear, may fragment with repeated removal and application. An insulation for the end unit of the fuel cell stack that does not need to be removed provides for faster and less costly repairs of the fuel cell stack.
The insulating wraps added to the end unit of the fuel cell stack do not militate against heat transfer within the end unit. A first portion of the cavities may be located on a first mating surface of the main body. The main body may be disposed against a second mating surface of another one of the main bodies, having a second portion of the cavities. The first portion and the second portion of the cavities may overlap when the main bodies are disposed against each other. An overlap of the cavities allow heat transfer from one of the main bodies to another one of the main bodies. Heat transfer during one of operation, startup, and restart of the fuel cell stack may result in a decrease in the efficiency of the fuel cell stack or an increase in time required for the fuel cell stack to reach the full operating potential. An insulation for the fuel cell stack that militates against heat transfer within the end unit may be desirable to increase the efficiency of the fuel cell stack and to decrease starting time
The insulating wraps added to the end unit of the fuel cell stack increase a manufacturing cost of the fuel cell stack and a vehicle into which the fuel cell stack is incorporated. The insulating wraps consume valuable space in vehicle applications. Additionally, a cost of manufacturing and shipping the insulating wraps is high when compared to the benefit the insulating wraps provide. A cost effective insulation may provide a desirable solution to an excessive cost of manufacturing and incorporating the insulating wraps.
There is a continuing need for an insulation for the end unit of the fuel cell stack that is compact and does not need to be removed for fuel cell stack repair. Desirably, insulation for the end unit of the fuel cell stack may also militate against heat transfer within the end unit and reduce the cost of insulating the end unit of the fuel cell stack.